Manufaturing Process

8/4/2019 Manufaturing Process

1/36


2/36

Process Encyclopaedia

Water jet cutting

Other names / variants: Hydrodynamic machining, Abrasive jet cutting

Overview

Jet cutting (or hydrodynamic machining) has been widely used in the food industry for a long

time, but more recently it being taken up by general engineering manufacturers.

The basic process is very simple a concentrated jet of fluid at almost supersonic velocity is

directed at the workpiece which literally blasts the material out of the cut.

In the food industry, oil is used which provides a hygienic means of cutting.

In metal cutting, fine abrasives in water are used steel up to 100mm thick can be cut

this way. All though the process is quite slow, sheets can often be stacked up and several cut at once.

The primary advantage for metal cutting is that the process generates very little heat, so the

material is not affected in any way.

Process details

Abrasive jet machining

An abrasive jet uses water that is pressurized up to 40,000 pounds per square inch (psi) and then forced

through a small sapphire orifice at 2500 feet per second, or about two and half times the speed of

sound.

Abrasive (often garnet) is then pulled into this high-speed stream of water and mixed with the water in

a long ceramic mixing tube. A stream of abrasive laden water moving at 1000 feet per second exits the

ceramic tube. This jet of water and abrasive is then directed at the material to be machined. The jetdrags the abrasive through the material in a curved path and the resulting centrifugal forces on the

particles press them against the work piece. The cutting action is a grinding process where the forces

and motions are provided by water, rather than a solid grinding wheel.

Materials and shapes

Abrasive waterjets can machine a wide range of thicknesses and materials, including metals,

plastics, glass, and ceramics.

Materials cut by the abrasive jet have a smooth, satin-like cut edge, similar to a fine sandblasted

finish.

Little heat in machining process.


3/36

Vacuum forming

Other names / variants: Thermoforming

Overview

Almost the opposite of blow moulding - with sucking instead of blowing! As a result, the two processes

are useful for different types of shape, although both can only produce parts with thin walls. This

process is more properly called thermoforming and relies on the sudden drop in strength and stiffnessof thermoplastics above a certain temperature.


Only suitable for thermoplastics and some polymer foams. Shapes should have constant section

thickness and not 'curve-back' on themselves. Parts cannot have holes or openings. Surface texturegood, but fine detail in mould cannot be copied. Suction holes in mould need to be small to avoid

leaving a mark on the product. Near-net-shape, but often leaves some waste material that needs

trimming (and is difficult to recycle).

Economics

Cycle time is limited by heating and cooling of the sheet. Normally cycle times of 5+ units a minute

can be achieved. Production rate can be increased by multi-part moulds, although extra trimming willbe required. Manual equipment is cheap enough to use in a school workshop. Fully automated

equipment can cost over 250,000. Moulds are usually aluminium (although wood can be used for

small-scale production) and so relatively inexpensive. Manual systems viable from 1 - 1000 parts. Withfully automated systems, only becomes economically viable for batches over 10,000.

Typical products

Advertising signs, bath panels, washing-up bowls, packaging.

___________________________________________________________________________________

Turning

Overview

Turning is unusual amongst the machining processes in that it is usually the workpiece that moves,

whilst the cutting tool remains stationary. Lathes in metalwork shops usually have single point cuttingtools. Lathes in woodwork shops often have tools with simple shapes to make turning of complicated

shapes more simple. Lathes in industrial woodworking have large, intricate cutting tools, capable of

shaping a complicated piece with only a few inserts of the tool.


4/36


Woods and metals are the most commonly turned materials, although difficulties arise with the

high-strength metals.

It is possible, but unusual, to turn polymers. Rigid polymer foams are sometimes turned when

producing models for prototypes.

Turning is usually used to produce parts with radial symmetry (i.e. based on a cylinder).

It is possible to produce other shapes, e.g. a helix or screw thread, by turning the part slowly and

moving the cutting head at a constant rate. Wood is the most commonly turned material, as it is easy to produce a wide variety of aesthetic

shapes.

Economics

The use of dedicated lathes for metal turning is rare on an industrial scale, except for

prototyping.

Where metal turning is required industrially, it is usually done as part of the function of a

machining centre.

Wood turning for mass production uses dedicated tooling to dramatically increase productionrates and hence reduce costs.

Typical products

Chair legs

bowls

candlesticks

large threaded shafts

___________________________________________________________________________________

Transformation hardening

Other names / variants: Laser hardening, Induction hardening, Flame hardening

Overview

Transformation hardening is often used in addition to carburising or nitriding, and is primarily used to

improve the mechanical properties of the surfaces of steel components. There are many ways to

"transform" the surface microstructure, but all of them involve heating of the surface followed by arapid quench (either in oil or water, or by a "self-quench" because the bulk of the component will stillbe cold).

Flame hardening uses a flame gun to provide the heating. It is inexpensive and flexible;

however it is quite slow, difficult to control accurately and not easily automated. Only external

surfaces can be treated.

Induction hardening works by placing the component in a high-frequency magnetic field. This

"induces" a current in the surface and so heats it rapidly. It can be used to uniformly treat largecomponents such as the rolls for a rolling mill. Although this process is expensive and requires


5/36

some dedicated tooling, it is easily automated and can be applied accurately e.g. to just theteeth on a gear cog.

Laser hardening works by focusing a laser beam on to the surface to provide very rapid

heating. As a result, a self-quench is usually sufficient. The equipment is very expensive and not

economic for large surfaces, but automation is straightforward and very precise control can be

achieved.

___________________________________________________________________________________

Surface treatment (generic)

Related processes in this database include:Case hardening, Transformation hardening, Surface

coatingPeening

Overview

Surface treatment processes apply primarily, but not exclusively to metals. After a component has beenformed and finished (e.g. by grinding), it may still not have acceptable surface properties. There are 4

main reasons why the surface properties may need altering:

1. Improve wearresistance.

2. Improve corrosion resistance.3. Improvefatigue resistance.

4. Change the aesthetic appearance.

There are various ways these aims can be achieved:

Coating the surface in a new material - e.g. painting, electroplating Altering the surface chemistry/microstructure e.g. carburising, transformation hardening

Changing the mechanical properties of the surface e.g. shot peening, planishing.

___________________________________________________________________________________

Surface coating (generic)

Other names / variants: Chemical vapour deposition (CVD), Physical vapour deposition (PVD),

Painting, Varnishing, Electroplating

Overview

By applying a surface coat of a different material, dramatic changes in the surface properties are

possible. Normally the materials used for the coats are too expensive, or have the wrong bulk propertiesto use for the whole components. There are several ways to coat the surface of a component:

Painting / varnishing. Commonly used to provide corrosion resistance for woods, but also

widely used for metals. Relatively inexpensive and flexible.
http://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/case_hardening.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/transformation_hardening.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/surface_coating.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/surface_coating.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/peening.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/transformation_hardening.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/surface_coating.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/surface_coating.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/peening.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/case_hardening.html


6/36

Electroplating is a relatively inexpensive way of providing a surface coat, although it relies on

the component being a good conductor and only certain coats are possible.

Physical vapour deposition (PVD) or sputtering works by "shooting" a fine spray of droplets

at the component. It is mainly used for metals and ceramics. Although very expensive, it canprovide excellent surface properties for high-performance drill bits etc.

Chemical vapour deposition (CVD) is similar to PVD, but the surface is formed by a chemical

reaction with a special gas rather than using a spray.

___________________________________________________________________________________

Soldering and brazing

Overview

Soldering and brazing differ from welding because only the filler melts, not the materials that are

joined. Soldering differs from brazing by the melting temperature of the filler alloy - this is usuallybelow 450oC for soldering and above 450oC for brazing. Soldering using lead-tin alloys was the first

hot joining process, used as far back as 4000BC.


Brazing is usually used for joining metals, and especially where the parts are not of the same material.

Most geometries are possible; however, good join alignment is essential to achieving a strong joint.

Mechanical cleaning or the use of flux is needed to give good joint strength. The strength of the joint is

also dependent on good design. Because of the low melting point of the filler, soldered joints havelimited use at high temperatures. Also, the joints are usually not strong and therefore not used in load-

bearing situations. Soldering aluminium and stainless steel is difficult because of their strong oxide

layers.

Economics

Equipment is generally low cost, except where automation is used. The need for good joint alignment

usually means fixtures are required, adding to the cost. Wave soldering is the most economic means ofsoldering large batches of printed circuit boards.

Typical products

Plumbing, electrical circuits


7/36

Sintering and HIPing

Overview

There are 2 main types of sintering: with pressure (hot pressing or pressure sintering) and without

pressure (pressureless sintering). A variant used for 3D shapes is called hot isostatic pressing (HIPing)Much of the research in powder processing is to obtain good quality powder, as this helps to achieve a

good quality component.


Mostly used for small (


8/36

design and quality. A wide variety of shapes can be made, but die design must account for the elastic'springback' of the sheet after forming. Some scrap is always produced and cannot be directly recycled.

Economics

Primarily used when near-net-shape processes are impractical in terms of time or materials e.g. for carbody panels. Simple manual equipment can cost only a few thousand pounds, but is only used for

prototyping and small batches as the production rates are low. Automated tooling (which can beexpensive) is usually dedicated to individual components, so is normally only used for long production

runs in order to be cost-effective. Production rates with automated equipment can be very high (drinkscans can be produced at almost a 1000 a minute).

Typical products

Cans, washing machine cases, car body panels, kitchen utensils, hubcaps, metal desks.

___________________________________________________________________________________

Sand casting

Other names / variants: green sand casting

Overview

Sand casting is the oldest form of casting and has been used for millennia.

It is still widely used today and in the US alone about 15,000,000 tonnes of metal are cast every

year. Although almost any sand can be used, a mixture of synthetic sand, clay and water, called green

sand, is preferred by most foundries.


Most metals can be cast, the limit is the melting temperature - the higher it is, the greater the

cost.

There is almost no limit to the size of a sand casting - casings over 5m wide are routinely made

(e.g. ship propellers).

Most shapes can be made, but the surface often has a characteristic rough finish which may

need machining.

Removing the extra material left from risers/gates etc. can also greatly add to the cost of the

finished product.

Porosity can be a problem leaving parts that are prone to cracking.


9/36

Economics

The basic equipment cost is low - from 500 to 3,000; automation and higher temperature

furnaces can increase this a lot. Dies can be cheap, but take some time to make.

The limit on the production rate is usually the cooling. Small parts can be produced at several an

hour - large parts can take hours or even days to cool fully.

The labour intensive nature of the process mean it is usually only economic for small batches,

although dedicated automation can increase this to 10,000+.

Typical products

Engine blocks

cylinder heads

pump housings

machine tool bases

ship propellers

___________________________________________________________________________________

Rotational moulding

Other names / variants: Rotomolding

Overview

Think of a large polymer product, and the chances are it is made by rotational moulding.

This versatile process is surprisingly inexpensive and is used to make a wide range of everyday

products. The main disadvantage is the low production rate which usually limits it to smaller batches.

Process details

Stage 1: Plastic is introduced to a mould in powder form up to the mass required for the requiredproduct.

Stage 2: The mould is then closed and passed into an oven chamber. The mould is then heated

externally to a temperature typically between 220C and 400C and is rotated around both vertical and

horizontal axes.

Stage 3: As the mould rotates, the inner surface passes through the mass of powder at the bottom of themould. As the mould heats up, the powder begins to melt and adhere to the inner surface of the mould.

The mould continues to rotate in the presence of heat and more plastic melts and builds up to produce

an even layer over the surface of the mould. The mould is then withdrawn from the oven whilst stillrotating and moved into a cooling chamber.

Stage 4: Cool air is directed at the mould and in some cases water jets are used to cool the mould.

When the plastic inside the mould has become solid, the mould can be removed from the cooling


10/36

chamber. The plastic component is then removed from the mould and allowed to finish the coolingprocess unrestricted by the mould.


Mainly for thermoplastics (especially polyethylene), but some thermosets can be used.

Used to produce containers and similar hollow products with uniform thin sections.

Tanks up to 4m across can be made this way; wall thicknesses as low as 0.4 mm are possible. Products are near-net-shape and rarely need further finishing.

Parts do not have to have circular cross-section.

The surface finish depends on the quality of the die surface; it is possible to include surface

detail such as logos.

Metal or polymer inserts can be moulded-in during processing.

All material is used in the product so there is no scrap.

Parts with large openings may be produced in pairs in a single mould and separated after

removal, or through use of insulation in mould.

The plastic is formed without pressure or centrifugal force and as such has no moulded in

stresses.

Economics

Cycle time is limited by heat conduction out of the mould, so increases dramatically for larger

wall thicknesses.

Thin walled products can be produced at almost 1 a minute, whereas thick walled products

might be as few as 3 per hour.

Although the tooling is dedicated, the moulds are usually quite cheap.

Equipment is relatively cheap - between 1 & 10 thousand pounds.

The long cycle times usually limit economic batch sizes to between 500 and 10,000.

Typical products

buckets

plastic footballs

dustbins

oil drums

storage tanks

traffic cones

___________________________________________________________________________________

Rolling

Other names / variants: tandem mill, reversing mill


11/36

Overview

Rolling was first used in the 1500s. The basic operation is a bit like flattening dough with a rolling pin.

Rolling is unusual in that it is primarily used for making stock items rather than making finished

components. Over 90% of worked metals are processed at some point by rolling.

Process details

Reversing mill

In a reversing mill, a hot ingot in moved back and forth through a set of connected die rolls.

Each roll gets closer the final shape, the last pass will finish the rolled shape.

Reversing mills are used for making thick sections such as slabs or large I-beams. In practice,

there do not need to be many separate dies (as is shown here) if the operator can move the

rolls closer together between passes.

Tandem mill

In a tandem mill, a hot slab is passed through a series of flat rolls.

Each of the rolls reduces the thickness slightly, until the desired thickness is reached. If the final

sheet is not too thick it can be coiled-up while it is still hot.

Tandem mills are mainly used for producing plate and sheet. In practice, 5 or more rolls in

series can be used in which case the material coming out the end can be going very fast!


For flat sections, ingots over 1m wide are reduced to plates (usually 6mm-300mm), sheet

(0.1mm - 6mm) or foil (about 0.008mm). Shaped sections (such as rails and I beams) up to 300 mm across are made using a series of

shaped rolls.

Specialised forms of rolling can be used to make large rings.

Hot rolling has poor dimensional tolerance and leaves a poor surface finish.

Cold rolling can improve these and also improve mechanical properties, but only for small

reductions in thickness.

Economics

For making stock items, rolling has few competitors.For this reason, it is usually performed bythe foundries before passing on to customers for further processing.

For long shaped sections, rolling is the only viable option for larger cross sections - for smaller

cross section extrusion may be more economic.

Machines can cost millions of pounds.

Typical products

I-beams, rails, sheets, plates, foil


12/36

Rapid prototyping (generic)

Other names / variants: Stereo-lithography, Selective laser sintering (SLS)

Overview

Prototyping is the making of a test component before full manufacture begins. These prototypes

provide an important means of assessing a design in a "hands-on" way. Conventionally, prototypingwas performed by machining the component from a solid block. With the advent of CAD/CAM and

CNC machining, this approach has greatly speeded up but "rapid" prototyping techniques are evenfaster. They all work by building-up thin layers in sequence to produce the whole component.

Recent trends in rapid prototyping include:

The techniques are now being used with scanning techniques to produce exact replicas of

delicate objects such as antique carvings.

Rapid mould development (rapid tooling), where prototypes produced by one of these

techniques is coated and can be used directly for injection moulding dies etc.

Making shapes not possible any other way e.g. custom jewellery, sculptures etc.

___________________________________________________________________________________

Powder metal forming

Other names / variants: Sintering, HIPping, Reaction bonding

Overview

One of the first uses for powder metal forming was the manufacture of tungsten filaments for

light bulbs. Advances in the technology mean even structural parts for aircraft (e.g. landinggear) can be made this way.

Much of the research in powder forming is to obtain good quality powder, as this helps to

achieve a good quality component.

Variants

Pressureless sintering involves only heat. It can be used for any shape.

Pressure sintering involves heat and axial pressure, but can only be used for 2D components. HIPping (hot isostatic pressing) is a variant used for 3D shapes; it uses a foil bag and a

hydrostatic pressure chamber.

Reaction bonding involves using a binder (so it can be moulded like plasticine) which is later

burnt off; it can used for most shapes.


Possible sizes range from balls in ball point pens up to 25kg.


13/36


14/36

Polymer extrusion

Overview

Unlike metal extrusion, polymer extrusion is a continuous process. A useful variation of the processcalled co-extrusion can be used (for example, to coat wires in-line for electrical cables). Polymerextrusion is sometimes used as a 'melter' for feeding other shaping processes such as injection

moulding or blow moulding.


Mainly used for thermoplastics, but can be used with rubbers and some thermosets. Complex shapes

with constant cross-section can be easily formed. Because of shrinkage, die design can be difficult (and

hence expensive) if good dimensional accuracy is required. Near-net-shape process, only the ends of

the extrusion are wasted.

Economics

The cost of the machines is high - well over 50,000. Die design can be expensive; the actual dies

usually cost a few thousand pounds to produce and need replacing after 10-100km of extrusion.Depending on size, parts can be extruded at rates from 1-60m/minute. Because of the high costs, it is

usually only economic to produce lengths over 10km - although there is little competition for many of

the possible shapes.

Typical products

Channels, pipes, sheet, architectural mouldings, cables, coated wires.

___________________________________________________________________________________

Peening

Other names / variants: Shot peening

Overview

Peening is only used for metals.

All metals can have their strength improved by working them i.e. deforming them past the

elastic limit. Peening only does this to the surface, by firing shot (like small ball-bearings) at

it. This can result in greatly improved fatigue resistance (useful for components which undergo

cyclic loading such as turbine blades).

Peening is flexible and relatively inexpensive unless significant automation is used.


15/36

Peening can also be used for shaping thin sheets but this isnt a surface treatment!

___________________________________________________________________________________

Milling

Overview

Milling will be familiar to anyone with experience of a metal workshop. The machines used

industrially can be extremely sophisticated - the cutting head is often able to twist and turn in manydirections! As well as being used for many small products suitable for school workshops, milling has

been used for large scale items such as aeroplane wings and tanks!


Almost any material can be milled, although difficulties arise with very brittle materials (e.g. ceramics)

and very hard materials (e.g. tool steel). Milling is used in metals primarily to shape parts by cuttingedges, slots or grooves. It is often used to complete parts that have been formed by a near-net-shapeprocess (e.g. casting or forging). Milling is unusual for wooden products, although variants such as

routing can be used to form grooves and mouldings.

Economics

Milling machines vary in price from 1,000 to 1,000,000. Milling is generally a very slow way to

produce a component - but it can be economic for prototyping or small batches. High speed machining

centres are used where the accuracy of milling is required to finish a component. The cost of milling on

a commercial scale is often a balance between higher speed and longer tool-life.

Typical products

Finishing surfaces (e.g. top of engine block), wooden furniture, architectural mouldings

___________________________________________________________________________________

Metal shaping (generic)

Related processes in this database include:Forging, Die Casting, Lost Wax Casting, Sand Casting,

Extrusion (metal), Rolling, Sheet forming

Overview

Bulk metal shaping is generally done near-net-shape by forging orcasting although further finishing
http://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/forging.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/die_casting.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/lost_wax_casting.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/sand_casting.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/metal_extrusion.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/rolling.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/forging.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/die_casting.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/lost_wax_casting.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/sand_casting.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/metal_extrusion.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/rolling.html


16/36

work is usually required. However, it does reduce the material wasted by machining and is usuallymuch faster. For many components, casting and forging are in direct competition and there is often no

easy way to decide which is the better choice; both are usually undertaken by specialist companies

(foundries and forges respectively).

There are a variety ofsheet forming processes suitable for metals less than 6mm thick, and in general

all products based on sheet will be made using one of these processes. Sheet is made by rolling, which

is also used to produce most large stock items held by material suppliers and a few final products such

as I-beams.

Extrusion is also used to produce some stock items with constant cross-section, such as tubes, andsome finished items, such as window frames.

___________________________________________________________________________________

Metal extrusion

Overview

Metal extrusion was developed in the late 18th century for making lead pipe. The basic process

of forcing a round billet through a shaped die is still used today.

Modern variants can produce clad products in one go - e.g. copper clad with silver.

Wire drawing is related to extrusion but is used for smaller (round) sections and the metal is

pulled through the die rather than pushed.


Mainly used with the softer metals, e.g. aluminium, copper, zinc. Generally speaking, the softer the metal, the more intricate the shapes that can be made.

Useful for long thin parts with constant cross-section.

Possible cross-sections are usually less than 100mm across.

Dimensional tolerance and surface finish may be poor with hot extrusion.

Cold extrusion is possible for some metals giving better properties.

Economics

Although extrusion appears to be a continuous process, it is really a batch process as it needs to

be interrupted to load new billets. Typical machine prices are in excess of 50,000.

Dies can cost upwards of 1000 to make (depending on size), but a lot more to design well.

More frequent die replacement is needed for higher strength metals.

Production rates from 5-10metres/minute are possible.

Usually only economic for several thousand metres +


17/36

Typical products

Tubing

aluminium window frames

railings

trims

wires

___________________________________________________________________________________

Mechanical fastening

Other names / variants: rivets, snap-fits, screws, bolts, nuts

Related processes in this database include:Joining (generic)

Overview

Mechanical joining falls into two distinct groups:fasteners and integral joints. Examples of fastenersinclude: nuts and bolts, screws, pins and rivets; examples of integral joints include: seams, crimps,

snap-fits and shrink-fits.

Some form of mechanical joining needs to be used where products need to be taken apart during their

normal life, e.g. where repair or maintenance is likely.

With the move towards efficient recycling, there is likely to be increased use of mechanical fastening.


Virtually any material in any shape can be joined by mechanical fastening - given enough

ingenuity!

Practical limitations come from being able to form holes - this limits the options for ceramics

and composites. Snap-fit joints are especially suitable for low stiffness materials like polymers.

Especially good for joining different materials (e.g. composite to metal).

Joint quality is reliable and readily determined, given sufficient operator skill. However,

mechanical joining usually reduces fatigue life.

Essential where two parts will move relative to each other (e.g. hinges for doors).

The non-permanence of many fasteners is useful for products that may need repair/maintenance

or need access to the interior.

Economics

Can be economic for any batch size from one-offs to mass production (with or without

automation).

Ease of mechanical joining (especially with snap fits) means low skilled workers can be used.

For fasteners, there can be a significant stock cost in ordering and keeping track of so many

components!
http://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/joining.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/joining.html


18/36


19/36

window frames

joists

architectural mouldings

___________________________________________________________________________________

Machining (generic)

Related processes in this database include:drilling, milling, turning, mechanical cutting, grinding,

polishing

Overview

Machining is one of the most widely used types of process found in industry, particularly for metals.

There are many variants including milling, grinding and drilling all share the common feature of

removing material with some form of cutting tool.

As it can be expensive, extensive machining of a product is limited to trials or low volume products. It

should be kept to a minimum for high volume products and so is not used for most consumer items.Industrially, milling, turning and drilling are often combined in CNC machining centres which can

produce a wide variety of shapes at high speeds. These machines can contain over 200 different cutting

tools, which are automatically replaced as they wear out.

It is possible (but unusual) to machine polymers care must be taken as they can melt. In addition,

machining polymers usually leaves a rough finish (they are normally smooth after moulding).

Mechanical cutting is a type of "machining" used to separate parts the most commonly know

processes are saws.

___________________________________________________________________________________

Lost wax casting

Other names / variants: Investment casting

Overview

Some form of lost wax casting has been used since 4000BC.

It is now mainly used for medium size batches where good quality is required.

The fine dust and harmful fumes require careful control of the workplace to avoid health

problems for operators.
http://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/drilling.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/milling.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/turning.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/mechanical_cutting.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/grinding_polishing.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/grinding_polishing.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/drilling.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/milling.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/turning.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/mechanical_cutting.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/grinding_polishing.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/grinding_polishing.html


20/36


Suitable for most metals, leaving a good surface finish which usually does not require further

finishing steps.

Best for small complex-shape parts, but can be used for parts from 5g to 100kg.

Not much metal scrap, and it can be easily recycled. Wax can be re-used but ceramic coating

must be disposed of carefully.

Economics

The production cycle is slow: usually only 1-5 castings can be made an hour, depending on the

size. Assembling lots of patterns on one tree can help in achieving a reasonable production rate.

The basic cost of the equipment can be as little as 1,000, although automated kit can be a lot

more. The cost of the patterns is usually only a few hundred pounds, but they can take several

weeks to make.

Although the setup costs are low, the low manual production rate means that only batch sizes of

up to 50 are economic; this can rise to a few thousand if automated.

Typical products

Jewellery

dental implants

hip replacements

valves

wind instrument keys

___________________________________________________________________________________

Laser processing (generic)

Overview

Although lasers are often thought of as "sci-fi", they are a surprisingly versatile tool in manufacturingand can be used for:

Cutting of most metals (up to 30mm thick) and woods. Over 75% of lasers are currently used

for sheet metal cutting as they can provide accurate cuts at high speeds. Because there is no

contact, it doesnt matter how hard the material is and there is no tool wear. Welding of most metals up to 20mm thick without the need for a filler. They can also be used

for high speed spot welding (used for Gillette razors).

Drilling of burr-free precision holes with no further finishing required. A common application

is the cooling holes in turbine blades it can be over 20x faster than competing techniques.

Surface hardening of steel component - see transformation hardening for further details.


21/36

Other applications include paint removal and rapid prototyping. Industrial lasers start at about100,000, but because they are very flexible and easily automated they can often prove cost-effective

___________________________________________________________________________________

Joining (generic)

Related processes in this database include:Welding, Brazing, Adhesive bonding, Mechanical

fastening

Overview

It is unusual for a product to be made in one-piece almost all products consist of components

which must be joined in some way.

The most familiar joining processes are probably mechanical fasteners and adhesives and, as a

result, designers often think they understand these the best. However, mechanical fasteningssuch as snap-fits are often over looked and modern adhesives are greatly under-rated becausethey are thought of as "just glue".

In addition to these processes, there are a variety of "hot processes" such as welding and

brazing which can often provide stronger and more economic joints for metal parts.

The one thing which is key for all the processes is to design the joint for the process, and not to

design the joint before deciding on the process a good joint for welding can be disastrous for

adhesive bonding, and vice-versa.

Joints are often a source of weakness in failure they are very important in design.
http://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/Weldinghttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/brazing.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/adhesive_bonding.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/mechanical_fastening.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/mechanical_fastening.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/Weldinghttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/brazing.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/adhesive_bonding.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/mechanical_fastening.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/mechanical_fastening.html


22/36


23/36

Production rates from 1-20 parts/minute are readily achievable.

Capital cost for machines are from 10,000 - 100,000 and dies can cost between 1,000 and

10,000.

Injection moulding is only economic for batches of 10,000 - 100,000 or more and so is usually

automated.

Typical products

toys,

model-making kits,

handles,

food containers,

cups,

electrical and plumbing fittings

___________________________________________________________________________________

Grinding / Polishing

Overview

The basic principle of grinding is similar to that of using sand paper to smooth wood. Where it is usedit will be the final finishing operation, with the possible exception of painting. Although grinding

wheels (which can be up to 2m!) are commonly found in industry, they are being replaced by abrasive

belts. Unusually for a mechanical process, grinding usually works best with harder materials, rather

than softer materials.


Grinding and polishing are finishing operations used where great dimensional accuracy or a good

surface finish are required. Polishing often produces a lustrous surface finish - this is due to softeningand smearing of the surface from the frictional heating. Primarily used with metals and ceramics.

Although grinding does remove material, almost none of this can be recycled.

Economics

On an industrial scale, the wear on grinding equipment is significant and this adds greatly to the cost.

The variable wear on a grinding wheel makes control of automated equipment more difficult and hence

expensive. The production rate depends on the level of finish required - the limiting factor is usuallythe overall cost. As with the other machining processes, grinding and polishing should be avoided if at

all possible


24/36

Glass forming

Overview

Sheet glass is produced by drawing, rolling, andfloating. Drawing is also used to produce fibres, rods

and tubes.

Discrete glass products (e.g. bottles) are made by blowing,pressingand casting.

All these processes begin with molten glass (which looks like red-hot thick syrup). A further process,calledsagging, is useful for products with shallow curves (e.g. plates) or light embossings.


There are over 750 types of glass, but they can all basically be formed in the same ways.

Drawing and rolling give a rough finish which normally needs grinding and polishing. Float

glass has a smooth surface.

A variant of drawing is used to make rods and tubes.

Blowing is used to produce hollow thin-walled items; it is similar to blow moulding of

thermoplastics. The surface finish is acceptable for most applications. Pressing produces parts with greater dimensional accuracy, but cannot be used for items with

thin walls or inward curves.

Economics

Production rates and costs strongly depend on the type of process and the size of component.

The different processes are generally suited to different shapes, so there tends to be little

competition.

Blowing of light bulbs takes place on expensive fully automated equipment, but over 1000

bulbs per minute can be formed. Fibre optics can be drawn at speeds of up to 500m/s.

Typical products

table tops

bottles

vases

television tubes

windows

headlights light bulbs

mirrors

dishes

optical fibres


25/36

Friction welding

Overview

Welding is commonly thought of as a process where material is melted - this type of process is more

properly called fusion welding. However, there is another type of welding process, called hot welding,where the material is heated until it softens but does not melt. Friction welding falls into the latter

category - the heating is provided by the rubbing of the parts to be joined (at speeds which can be up to15m/s).


Usually, at least one of the parts to be joined must be circular - this can be solid or hollow.

One of the materials to be joined must soften before melting.

Used to join different materials to each other (e.g. polymers to metals).

Solid bars up to 100mm can be joined and pipes up to 250mm.

Good joint quality depends on good alignment of parts and timing of the final forging together.

Economics

Basic equipment costs around 10,000, but automation can increase this significantly.

Most suited economically to joining pipes and attaching studs.

For similar metals, competitive with arc welding for the geometries it can do. But because of the

capital cost, it is not competitive where only a small number of joints are required.

Competitive with adhesives for polymers for the geometries it can do, especially for a large

number of joints.

Removal of flash (if required) adds to the cost.

Typical products

pipes

studs

___________________________________________________________________________________

Forging

Other names / variants: ring-rolling, open-die forging, closed-die forging, drop forging

Related processes in this database include:metal extrusion

Overview

Forging is probably the oldest metalworking process - dating back to at least 5000BC.

It has advanced a long way from its "blacksmith" image and today there are many hi-tech

variants that compete mainly with the casting processes.
http://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/metal_extrusion.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/metal_extrusion.html


26/36

Although forging can take place "cold", the component is usually heated to reduce the forces

required.

The forging action can be extremely noisy!

Variants

Impression Die Forging - also called closed die forging, presses metal between 2 dies that

contain a precut profile of the desired part. Cold Forging - includes bending, cold drawing, cold heading, coining, extrusions and more, to

yield a diverse range of part shapes. The temperature of metals being cold forged may range

from room temperature to several hundred degrees.

Open Die Forging is performed between flat dies with no precut profiles is the dies. Movement

of the work piece is the key to this method. Larger parts over 20 tonnes and 10 metres in length

can be hammered or pressed into shape this way.

Seamless Rolled Ring Forging is typically performed by punching a hole in a thick, round

piece of metal (creating a donut shape), and then rolling and squeezing (or in some cases,pounding) the donut into a thin ring. Ring diameters can be anywhere from a few inches to 30

feet.

Process details

Closed-die forging

A heated blank is placed between 2 halves of a die


27/36

A single compressive stroke squeezes the blank into the die to form the part. In hammeror drop forgingthis happens

by dropping the top of the mould from a height. An alternative is to squeeze the moulds together using hydraulic

pressure.

Once the die halves have separated, the part can be ejected immediately using an ejector pin.


28/36

The waste material, flash, is removed later.


Any metal can be forged, provided the blank is hot enough (( 60% of the melting temperature).

Typical possible sizes for closed dies range from 10g to 10kg, depending on complexity.

The part is left with good surface and mechanical properties, although cold-forging can performeven better.

Complex parts can be formed using a series of forging dies with increasing levels of detail.

A draft (taper) angle has to be incorporated to allow easy removal of the part.

Any waste material squeezed between the die halves, called flash, is readily recycled.

Economics

Production rate is limited by the insertion and removal of the blank, so some form of

automation is often used.

As a result, machines can cost 100,000+, but can produce many parts a minute (if small). As both the machines and the dedicated dies are costly, production runs in excess of 50,000 are

often needed to produce small parts economically.

Large parts can be produced economically at smaller batch sizes, because there is less

competition.

Typical products

Spanners


29/36

pedal cranks

gear blanks

valve bodies

hand tools

crankshafts

coins

___________________________________________________________________________________

Drilling

Other names / variants: Trepanning

Overview

One of the most common of the machining processes - as there are few other ways to produce a deep

circular hole. One of the biggest challenges to the drill designer is how to remove the waste material

out of the hole at the same time as getting the cutting fluid into the hole. Large shallow holes are madeby trepanning, where a disc is removed rather than all the material.


Almost any material can be drilled, although difficulties arise with very brittle materials (e.g.

ceramics) and very hard materials (e.g. tool steel).

Drilling is used for making circular holes, dimensional accuracy can be improved by subsequent

reaming or boring.

Holes from 0.5 mm to 50mm are commonly drilled - although the design of the drill bit will

vary quite a lot! Drilling is often used to complete parts that have been formed by a near-net-shape process (e.g.

casting or forging) as precision holes are difficult to form with these processes.

Threaded holes are made by first drilling a cylindrical hole and then "tapping" with a threaded

cutting tool.

Economics

It is normal to try to reduce the amount of drilling required in a component by careful design -

but when an accurate hole is required, drilling has little competition.

Where drilling is required industrially, it is usually done either as part of the function of amachining centre, or in a dedicated drill set with multiple heads so that all the holes can bemade simultaneously

___________________________________________________________________________________

Die casting

Other names / variants: ferro-die casting


30/36

Overview

Developed in the early 1900s, this is the most common of the casting processes that use a

permanent mould.

It is used for high volume products, of which small zinc die-cast toys (e.g. "Matchbox" cars) are

probably the most widely known.

Very small components like zipper teeth can be made at over 20,000 an hour!

Variants:

Ferro-die is used for high melting point materials such as steels. It uses higher melting point ferrous

alloys for the die materials and is more expensive.


Mostly used for low melting point alloys such as aluminium, zinc and copper. In general only

small parts are made, but it can be used for components up to 25kg.

Complex parts can be made with good dimensional accuracy and surface detail. A draft (taper) angle has to be incorporated to alloy easy ejection of the part.

Parts are left with good mechanical surface properties.

Ejector pin marks are often visible.

Economics

The machinery is expensive, and can cost well over 100,000.

Dies cost many thousand pounds and need to be replaced after a few hundred thousand uses.

They can take several weeks to manufacture, mean prototype testing is slow.

The production rate depends on how long the part takes to cool before it can be ejected. Thiscan give rates of 500+ parts per hour in normal conditions.

Because of the high capital cost, the process is only economic for batches of 100,000+

Typical products

Small toys e.g. cars/soldiers

hand tools

disc drive chassis

motor casings

carburettors


31/36

Compression moulding

Overview

Essentially, this process is forging for polymers - although only one 'hit' is possible. Mainly used for

thermosets and rubbers in mid-size batches as injection moulding is cheaper for thermoplastics. Withthermosets, the chemical reaction provides most of the heat, so little extra energy is required.


Mainly used for thermosets, although rubbers, some thermoplastics and chopped-fibre composites canbe formed this way. Limited to simple shapes, although a wider variety is possible with rubbers as they

can be more easily removed from the mould. Possible part size range from 10mm up to 1m. Waste

material, called flash, needs to be removed after moulding and is not readily recycled.

Economics

Cycle time is limited by heat transfer, or curing time and is usually over 1 minute. Production rate can

be increased by using multiple cavity moulds. Equipment cost is low compared to similar processes -

about 10,000 - 50,000. Die cost a few thousand pounds, and need replacing after 10-50,000 uses. Thelow production rate means that it is only usually economic for batch sizes in the tens of thousands.

Typical products

Dishes, handles, caps, electrical components.

___________________________________________________________________________________

Composite shaping (generic)

Overview

The unique structure of reinforced plastics requires special processes to shape them into useful

products. Although some of the polymer forming processes can be used (when the fibres are choppedand mixed in a polymer), there are special processes which are specific to composites containing long,

continuous fibres (such as CFRP) it is these that are discussed here. Many of the polymer resins used

can give off toxic fumes, so precautions have to be taken to protect operators from the adverse effects.Design issues include:

Avoiding sharp changes in section

Orienting fibres where possible to improve mechanical properties

Forming as close as possible to finished shape; drilling holes can dramatically reduce strength


32/36


33/36

Typical products

Boat hulls, propeller blades, baths, water tanks, structural cables, rocket noses, turbine blades, golf

clubs, tennis racquets, bicycle frames

___________________________________________________________________________________

Ceramic shaping (generic)

Related processes in this database include:glass moulding, sintering, HIPping

Overview

There are several ceramic forming processes, although most of them are specific to individual materials

such as throwingfor pottery, castingfor concrete andslip castingfor porcelain.

Because ceramics only melt at very high temperatures, most forming of engineering ceramics (likealumina) is based on using dry powder or "bound" powder which can be moulded; at the dominant

method of forming engineering ceramics is sintering. An exception to this general rule is glass

forming, since glass softens sufficiently for it to be moulded.

Case hardening

Other names / variants: Carburising, Nitriding

Overview

Carburising and nitriding are both forms of case hardening and are primarily used to improve the

mechanical properties of the surfaces of steel components. The component to be treated is put into aspecial gas atmosphere (gas carburising) at a high temperature. The process works by altering the

surface chemistry because of the diffusion of gas into the solid.

The process is quite slow because it depends on diffusion, so it is normally automated by using aconveyor belt. It is also possible to use certain liquids (liquid carburising) which speed up the diffusion

so cycle times are shorter.

The main advantages of these processes are:

only simple equipment is required and no dedicated tooling,

and any shape can be treated, as long as the gas has a passage to the surface,

large components can be treated in one go

the main disadvantages are:

relatively slow,
http://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/glass_moulding.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/sintering.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/glass_moulding.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/process_encyc/non-IE/sintering.html


34/36

not easy to transform only parts of the surface

Blow moulding

Overview

Blow moulding is most commonly a batch process used to produce simple drinks bottles. Clever designof the blank allows the screw top and base of bottles to be thicker than the walls.


Used for simple, thin-walled, hollow products - mainly bottles

Used with thermoplastics, mainly PET.

Good, smooth surface finish can be readily achieved.

Depending on how the hollow blank (parison) is made, scrap can be negligible.

There is a variant which is continuous and used to produce thin-walled tubes which can be slit

to make cling-film or plastic bags.

Economics

The production speed is limited by opening and closing the mould, so automation is normally

used.

Production rates from a few hundred to a few thousand per hour can be achieved.

The tooling and machines are moderately expensive (10,000 - 100,000).

Moulds may need to be replaced after about 100,000 uses.

Only used for high volume products with batch sizes of 100,000+.

Typical products

Bottles and containers up to 0.5 litre

Arc welding

Other names / variants: MMA, TIG, MIG, spot welding, seam welding

Overview

There are several types of arc welding - MMA (Manual Metal Arc) is probably the most well


35/36

known. Automated arc processes include TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas).All arc processes use afillerto join the two pieces - in MMA and MIG the filler also serves as

the electrode which makes the electric arc.

There are other more specialist arc welding processes such as spot welding orseam welding

which work without a filler.

Safety precautions must be taken to protect the welder from the bright arc and the noxious

fumes.

Good welding requires a lot of skill, and in industry a welder must have special qualifications.


Although many metals can be joined with MMA, it is most commonly used for steel. Other

materials, such as aluminium, are usually joined by more sophisticated arc welding processes(e.g. MIG, TIG).

MMA is portable and so suitable for repair or on-site work.

Thin plates may require only one pass for a successful join. For thicker plates, multiple passes

may be required to fill the gap.

For thin plates, the edges may be square. For greater thicknesses, the edges need to be bevelled

to allow the gap to be filled more easily. In the area that has been affected by heat, the properties of the material may change greatly.

Economics

The cost of MMA equipment can be less than 100. However, the production rate is slow so it

is only economic for one-off jobs, repair work and difficult access situations.

MIG and TIG are available as manual processes, but they are often automated to improve

quality and production rate.

For joining thick metals, arc welding has few serious competitors.

Where reliable joints are essential (e.g. aeroplane wings) mechanical fasteners such as rivets areused instead of welding.

Joining of sheet (e.g. car body panels) is usually more economic by other welding processes

such as spot welding.

Typical products

Car bodies

ships

oil rigs

pipelines pressure vessels

Adhesive bonding

Overview

Adhesive bonding was first used for load-bearing joints for aircraft in World War II. Significant


36/36

advances have been made in the technology since then, but it has still to be widely used industrially formetals. Adhesives are available in many forms including: liquids, pastes, powders, tapes and films.

Adhesive bonding is often combined with mechanical joining - 'super glue' was first used to prevent

nuts on machinery shaking loose.


Any materials can be joined, although some may require special surface preparation. Especially usefulfor joining different materials or very thin materials. The mechanical properties of adhesive joints can

be very good, but they usually have poor resistance to 'peeling'. The strength also deteriorates withtemperature and is rarely useful above 100-2500C. Adhesive joints can provide additional benefits as

well as joining, including: sealing, insulation, corrosion protection and vibration damping. Correct

design of the joint is essential for it to be strong. One method is to increase the area, so lap joints arebetter than butt joints; another solution is to design interlocking joints and combine with another form

of mechanical joining.

Economics

Equipment costs (unless automation is required) can be low, although the cost of the adhesives

themselves can be significant. Where good joint quality is essential, special equipment such as fixtures,

presses and ovens are required which can significantly add to the cost. The production rate is oftenlimited by the curing time, which can range from a few seconds to many hours (think of 'super glue'

and 'araldite' as common household examples).

Typical products

car mirrors, brake linings, helicopter blades, laminated glass, packaging.

Manufaturing Process

Documents

Transcript of Manufaturing Process